Doped and un-doped vanadium dioxide thin films prepared by atmospheric pressure chemical vapour deposition from vanadyl acetylacetonate and tungsten hexachloride: the effects of thickness and crystallographic orientation on thermochromic properties

The atmospheric pressure chemical vapour deposition reaction of vanadyl acetylacetonate and tungsten hexachloride with oxygen led to the production of thin films of tungsten doped monoclinic vanadium dioxide on glass substrates. Scanning electron microscopy and X-ray diffraction indicated that the films had different morphologies and crystallinities depending on the deposition conditions used. Transmission and reflectance measurements showed a significant change in properties in the near infra-red either side of the metal to semiconductor transition. Variable temperature transmission studies show that the metal to semiconductor transition was lowered by tungsten doping. The effect of film thickness was studied with un-doped and doped films. It was found that film thickness limited the intensity of light passing through the film and the extent of the thermochromic transition but was found not to influence the hysteresis width or temperature of transition. Different film growth conditions led to a range of film morphologies which profoundly affected the resulting optical properties of the films. It was found that film morphology and preferred crystallographic orientation had a marked influence on the width and switching temperature of the thermochromic transition.